1. Field of the Invention
The present invention relates to a heat sink used for a semiconductor element in a Large Scale Integrated Circuit (LSI) of high testing density provided in a microcomputer driven at high speeds, and also relates to a heat sink used for a semiconductor element used for a thyristor of middle capacity and a power transistor. More particularly, the present invention relates to an air-cooled type compact heat sink in which generated heat is dispersed by air for cooling.
2. Related Art
FIG. 13 is a perspective view and FIG. 14 is a side view of a conventional heat sink mounted on a QFP (Quadrangle Flat Package) type heat generating body (LSI) of a ceramic package. In FIGS. 13 and 14, numeral 90 is a heat sink made of highly heat-conductive material such as aluminum and copper. The heat sink 90 is manufactured by means of machining so that a fin portion 92 is formed in the periphery of a heat-conductive support portion 91. A central portion of the heat-conductive support portion 91 is closely contacted with and mounted on a central surface of the QFP type LSI 93 which is a heat source. Therefore, heat generated by the LSI 93 is radiated by the fin portion 92.
In the heat sink 90 constructed in the manner described above, unless the diameter dl of the fin portion 92 is extended or the number of the fins is increased in accordance with the increase of heat generated by the LSI 93, that is, unless the surface area of the fin portion 92 of the heat sink 90 is increased, sufficient heat radiating effects can not be provided. However, in the case where the diameter d1 of the heat sink 90 becomes larger than the outer diameter of the LSI 93, or in the case where the height H of the heat sink 90 is increased too much, the significant problems may be encountered. When such a large heat sink 90 is disposed in a limited small space in an electronic apparatus, convection of air is obstructed, so that the cooling capacity is remarkably lowered.
Even when it is permitted that the dimensions of the heat sink 90 are increased, in the case where the diameter dl of the fin portion 92 is simply extended or the number of the fins is simply increased, a distance from the heat source (LSI 93) is increased, so that the heat resistance of the material composing the heat sink 90 is increased. Therefore, it is necessary to increase the thickness t1 of the fin, and to extend the diameter d2 of the heat-conductive support 91. Accordingly, as a measure to be taken against the increase of heat generated in the LSI not only the dimensions of the heat sink are increased but also a large capacity of motor to drive a cooling fan is employed for a forced convection. Consequently, the costs are raised.
The machining of the heat sink 90 is also restricted by the heat sink material, mechanical strength of the cutting tool and cutting accuracy, thus, a ratio of the diameter d2 of the heat-conductive support 91 to the diameter d1 of the fin portion 92 is limited since the fin interval t2 necessary for an appropriate convention must be maintained. For this reason, when the heat sink 90 is made compact, the reduction of thickness t1 of the fin is limited.
Further, in the conventional heat sink 90, it is necessary to provide the heat-conductive support 91. Therefore, heat is accumulated among closely stacked fins under the condition of a natural convection or a gentle wind so that heat is not effectively radiated.